The present invention relates to a liquid filtration system, and more particularly to a filtration monitor system for an open loop fluid system.
While most aircraft fuels are subject to stringent quality standards, storage and refueling equipment may contaminate the high quality fuel with contaminants. This contamination may still occur even though efficient filtration and water separating equipment is utilized whenever fuel is transferred from one point to another. Considering the potential variability of fuel supplies, aircraft typically include an internal fuel filter system to further assure that only acceptable fuel is supplied to the aircraft engines.
Fluid filter systems typically become contaminated and clogged over time. In most cases the filters are replaced on a periodic basis as part of routine maintenance. In some filter systems, a differential pressure-sensing device provides a mechanical or electrical indication the filter is clogged and a bypass valve around the filter was tripped to allow continued operation with the clogged filter. This practice results in operation without filtration of the fluid, creating the possibility of component contamination.
In closed fluid systems, which operate on a fixed supply of fluid with limited fluid additions (such as gearbox lubrication systems), the rate of debris accumulation may be minimal and the filter element will last the life of the equipment barring an extraordinary event. In open systems with a continuous through flow (such as fuel delivery systems), the rate of contamination buildup is directly dependent on the quality of the fuel supply.
Although filter elements are replaced on a routine basis, the replacement interval is typically conservatively specified, due to varying operating conditions which may result in unnecessary maintenance and an unneeded expense. In particular, aircraft are rotated through a maintenance cycle on a predetermined scheduled interval. As the scheduled interval does not typically correlate with a filter contamination rate (due to fuel contaminant variability), the filter elements are often replaced as a matter of routine to always assure a proper functioning filter. This may further increase the scheduled maintenance expense.
Conventional filter monitoring systems often utilize a mechanical differential pressure monitor with a thermal lockout that prevents the device from actuating due to the increased viscosity of a cold fluid. This type of monitoring system triggers an electrical switch and/or a visual indicator when a predetermined ΔP reaches a trigger level. The trigger level is typically set around 80% of the level that would result in filter bypass or clogging as the equipment needs to be operable for a specified period of time following the trigger to conveniently schedule required maintenance.
Disadvantageously, such conventional monitoring systems are mechanical and may fail due to vibration and pressure oscillations; the interval between trigger indication and eventual clogging or bypass varies with the level of new contaminant introduction; and extraordinary contamination events are undetected until the trigger level is reached.
Accordingly, it is desirable to provide a filter system that monitors the filter element to determine when the filter element is expected to reach a particular clogged level to more closely correlate filter replacement with a maintenance schedule to minimize expense and increase resource efficiency.